Valve measurements

I have a number of 211 valves which I had tested a while back. Results are shown as relative gain say 950 and current say 56.

When I look at adverts for 211s they are shown as ma and GM say 118 and 4500. No doubt a numpty question but how do I reconcile these ?


Short answer - you can’t. The numbers are tester specific, you need to know what a good value is for te specific tester.

Pete’s right. The results of the test depend on the conditions under which you carried out the test. Like if you’re measuring, say, engine power - it depends on the rev rate you’ve chosen and on the octane rating of the fuel you’ve used.

The people who manufactured the valve will have given, in the data sheet, the anode current (measured in mA) and the transconductance (called the GM, measured in mA/V) that a valve in good condition should have under a certain set of test conditions.

The 211 datasheet here says (middle of the three columns towards the bottom of the page) that if you apply an anode voltage of 1000V and a grid voltage of -61V then you should measure an anode (also called plate) current of 53mA and a GM of 3150 umhos which is equivalent to 3.15mA/V.

But you can see from the columns on either side that if you use a different anode and grid voltage then you will get a different anode current and GM. Unless you know what anode and grid voltage the tester used you can’t tell what their results mean in terms of the valve’s condition. You can, to an extent, tell whether two valves match though.



Ahh, I was hoping to buy valves that match up with some of my existing ones.

If you can find a co-operative seller you might send him the valve you want to match and ask him to test it on his tester. Then he can pick a matcher from his stock.


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